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Wolves

Yellowstone National Park ensures the long-term viability of wolves in Greater Yellowstone and provides a place for research on how wolves may affect many aspects of the ecosystem.

NPS / Jim Peaco

Although wolf packs once roamed from the Arctic tundra to Mexico, loss of habitat and extermination programs led to their demise throughout most of the United States by early in the 1900s. In 1973, the US Fish and Wildlife Service listed the northern Rocky Mountain wolf (Canis lupus) as an endangered species and designated Greater Yellowstone as one of three recovery areas. From 1995 to 1997, 41 wild wolves from Canada and northwest Montana were released in Yellowstone National Park. As expected, wolves from the growing population dispersed to establish territories outside the park where they are less protected from human-caused mortalities. The park helps ensure the species’ long-term viability in Greater Yellowstone and has provided a place for research on how wolves may affect many aspects of the ecosystem.

Wolves (back) are larger than coyotes (middle) and red foxes (front).

NPS / Michael Warner

Description

Wolves are highly social animals and live in packs. Worldwide, pack size will depend on the size and abundance of prey. In Yellowstone, average pack size is 10 individuals. The pack is a complex social family, with older members (often the alpha male and alpha female) and subordinates, each having individual personality traits and roles within the pack. Packs defend their territory from other, invading packs by howling and scent marking with urine.

Wolves consume a wide variety of prey, large and small. They efficiently hunt large prey that other predators cannot usually kill. In Yellowstone, 90% of their winter prey is elk; 10–15% of their summer prey is deer. They also kill bison.

Many other animals benefit from wolf kills. For example, when wolves kill an elk, ravens arrive almost immediately. Coyotes arrive soon after, waiting nearby until the wolves are sated. Bears will attempt to chase the wolves away, and are usually successful. Many other animals—from magpies to invertebrates—consume the remains.

Changes in Their Prey

From 1995 to 2000, in early winter, elk calves comprised 50% of wolf prey and bull elk comprised 25%. That ratio reversed from 2001 to 2007, indicating changes in prey vulnerability and availability. The discovery of this change emphasizes the importance of long-term monitoring to understand predator-prey dynamics. Changes in wolf predation patterns and impacts on prey species like elk are inextricably linked to other factors such as other predators, management of ungulates outside the park, and weather (e.g. drought, winter severity). Weather patterns influence forage quality and availability, ultimately impacting elk nutritional condition. Consequently, changes in prey selection and kill rates through time result from complex interactions among these factors. Current NPS research focusses on the relative factors driving wolf predation over the last two decades.

Number

An estimated 528 wolves resided in the Greater Yellowstone Ecosystem as of 2015.

As of December 2016, there were at least 108 wolves in the park. Eleven packs were noted.

In general, wolf numbers have fluctuated between 83 and 108 wolves from 2009 to 2016.

Where to See

They inhabit most of the park, peak activity is at dawn and dusk.

The northern range of Yellowstone is one of the best places in the world to watch wolves.

Size and Behavior

26–36 inches tall at the shoulder, 4–6 feet long from nose to tail tip.

Males weigh 100–130 pounds, females weigh 80–110 pounds.

Home range within the park is 185–310 square miles (300– 500 km2); varies with pack size, food availability, and season.

Average lifespan in the park is 4–5 years. Average lifespan outside is 2–3 years. The oldest known wolf to live here was 12.5 years.

Two main color variations exist in Yellowstone in approximately equal proportions: black and gray.

Prey primarily on hoofed animals. In Yellowstone, 90% of winter diet is elk; summer prey consist of more deer and smaller mammals.

Mate in February.

Give birth to average of five pups in April after a gestation period of 63 days.

Young emerge from den at 10–14 days; pack remains at the den for 3–10 weeks unless disturbed.

Leading cause of death for wolves within the park is death by other wolves.

Leading cause of death for wolves outside the park is human-caused.

Interesting Wolf Behavior

Wolves kill each other and other carnivores, such as coyotes and cougars, usually because of territory disputes or competition for carcasses. In 2000, however, the subordinate female wolves of the Druid pack exhibited behavior never seen before: they killed their pack’s alpha female; then they carried her pups to a central den and raised them with their own litters.

The Northern Range is the hub of wildlife in Yellowstone National Park. Occupying just 10 percent of the park, it is winter range for the biggest elk herd in Yellowstone and is arguably the most carnivore-rich area in North America. Early management of predators caused dynamic changes to the ecosystem. The reappearance of carnivores on the landscape has had significant and sometimes unexpected impacts on the resident grazers and their habitat.

Historical and current range of gray wolves.

NPS

Population

In the first years following wolf restoration, the population grew rapidly as the newly formed packs spread out to establish territories with sufficient prey. The wolves have expanded their population and range, and now are found throughout the Greater Yellowstone Ecosystem.

Disease periodically kills a number of pups and old adults. Outbreaks of canine distemper have occurred in 2005, 2008 and 2009. In 2005, distemper killed two-thirds of the pups within the park. Infectious canine hepatitis, canine parvovirus, and bordetella have also have been confirmed among Yellowstone wolves, but their effect on mortality is unknown.

Sarcoptic mange, an infection caused by the mite (Sarcoptes scabiei), reached epidemic proportions among wolves on the northern range in 2009. The mite is primarily transmitted through direct contact and burrows into the wolf’s skin. This process can initiate an extreme allergic reaction and cause the wolf to scratch the infected areas, which often results in hair loss and secondary infections. By the end of 2011, the epidemic had mostly subsided; however, the infection is still currently present at lower prevalences throughout the park.

Wolf packs are highly territorial and communicate with neighboring packs by scent-marking and howl- ing. Occasionally packs encounter each other and these interactions are typically aggressive. Larger packs often defeat smaller groups, unless the small group has more old adult or adult male members. Sixty-five percent of collared wolves are ultimately killed by rival packs.

Greater Yellowstone wolf population, 1995–2016

NPS

The park’s wolf population has declined substantially since 2007, when the count was 171. Most of the decrease has been in packs on the northern range, where it has been attributed primarily to the decline in the elk population and available territory. Canine distemper and sarcoptic mange have also been factors in the population decline.

Each year, park researchers capture a small proportion of wolves and fit them with radio tracking collars. These collars enable researchers to gather data on an individual, and also monitor the population as a whole to see how wolves are affecting other animals and plants within the park. Typically, at the end of each year, only 20% of the population is collared.

Wolves in the Northern Rocky Mountains have met the US Fish and Wildlife Service’s criteria for a recovered wolf population since 2002. As of December 2015, the US Fish & Wildlife Service estimated about 1,704 wolves and 95 breeding pairs in the Northern Rocky Mountain Distinct Population Segment.

The gray wolf was removed from the endangered species list in 2011 in Idaho and Montana but is currently protected as endangered species in the state of Wyoming. Wolves are hunted in Idaho and Montana under state hunting regulations.

Wonders abound in Yellowstone, though many come with an unfamiliar danger. Learn how to adventure through Yellowstone safely.

Wolf territories in Yellowstone (2016)

NPS

Your Safety in Wolf Country

Wolves are not normally a danger to humans, unless humans habituate them by providing them with food. No wolf has attacked a human in Yellowstone, but a few attacks have occurred in other places.

Like coyotes, wolves can quickly learn to associate campgrounds, picnic areas, and roads with food. This can lead to aggressive behavior toward humans.

What You Can Do

Never feed a wolf or any other wildlife. Do not leave food or garbage outside unattended. Make sure the door is shut on a garbage can or dumpster after you deposit a bag of trash.

Treat wolves with the same respect you give any other wild animal. If you see a wolf, do not approach it.

Never leave small children unattended.

If you have a dog, keep it leashed.

If you are concerned about a wolf—it’s too close, not showing sufficient fear of humans, etc., do not run. Stop, stand tall, watch what the wolf is going to do. If it approaches, wave your arms, yell, flare your jacket, and if it continues, throw something at it or use bear pepper spray. Group up with other people, continue waving and yelling.

Report the presence of wolves near developed areas or any wolf behaving strangely.

To date, eight wolves in Yellowstone National Park have become habituated to humans. Biologists successfully conducted aversive conditioning on some of them to discourage being close to humans, but two have had to be killed.

Predator-prey chases happen countless times every day in Yellowstone, but we rarely witness them. Kira Cassidy, research associate with the Yellowstone Wolf Project, provides context and insight as a wolf tests an elk along Soda Butte Creek.

Hebblewhite, M. and D.W. Smith. 2010. Wolf community ecology: Ecosystem effects of recovering wolves in Banff and Yellowstone national parks. In M. Musiani, L. Boitani, and P. Paquet, editors, The world of wolves: new perspectives on ecology, behavior and policy. Calgary: University of Calgary Press.